Search

We have reported on a new method for obtaining a liquid-metal field emitter. The treatment of a porous crystal of GaP binary semiconducting compound with high-voltage pulses in a vacuum has made it possible to obtain stable structures on its surface in the form of discrete gallium clusters. These structures exhibit high emission properties, including stable currents at a level of a few microamperes, as well as the high uniformity of the distribution of emission nanocenters over the surface. [ABSTRACT FROM AUTHOR]

Three open-framework gallium phosphates [C6H16N2][Ga(HPO4)(PO4)] (1), {H[C6H16N2]2[Ga7(OH)2(PO4)8]} (2), and {H[C4H12N2]2[Ga7(OH)2(PO4)8]·2H2O} (3) were solvothermally synthesized in the presence of 2,6-dimethylpyrazine, N-ethylpiperazine, and piperazine as templates, respectively. Compound 1 possesses an infinite one-dimensional chain structure connected by hydrogen-bond interactions to generate a 3D supramolecular framework. Compounds 2 and 3 show similar inorganic framework structures, which may be viewed as the assembly of a secondary building unit (SBU), Ga6P8 containing two GaO4, two GaO5, two GaO6 as well as eight PO4 groups. The SBUs are linked with each other by vertexsharing oxygen atoms to form 2D sheets, which are further connected by GaO4 tetrahedra to result in the final 3D open-framework with leftand right-handed helical chains. In these materials, the well-ordered organic species reside in the voids of structures and interact with the framework by way of hydrogen bonds. [ABSTRACT FROM AUTHOR]

We report on the optical generation and detection of ultrashort acoustic pulses that propagate in three-dimensional semiconductor crystals. Photoexcitation of lattice-matched GaP layers grown on Si(001) gives rise to a sharp spike in transient reflectivity due to the acoustic pulse generated at the GaP/Si interface and detected at the GaP surface and vice versa. The extremely short width of the reflectivity spike, 0.5 ps, would translate to a spatial extent of 3 nm or 10 atomic bilayers, which is comparable with the width of the intermixing layer at the GaP/Si interface. The reflectivity signals are also modified by quasi-periodic Brillouin oscillations arising from the propagation of the acoustic pulses in the GaP and Si crystals. The present results demonstrate the potential applications of the simple optical pump-probe scheme in the nondestructive evaluation of the buried semiconductor interface quality. [ABSTRACT FROM AUTHOR]

A novel multi-junction GaP/InP/Si solar cells with improved p++AlGaAs/n++ AlGaAs tunnel junction model is designed using the Synopsys/RSoft/Solar cell utility software. The optical and electrical simulations of this cell are performed using the 2D full-wave and solar cell utility, resulting in an open circuit voltage of 3.02 V, short circuit current density of 15.942 mA/cm2, fill factor of 82.7%, and power conversion efficiency of 44.23%. Then, an optimization study of a function of variation in thickness of different layers is performed. Simulation results of the optimized structure under AM 1.5G condition showed a small improvement in the short circuit current density by 0.38%, efficiency by 0.375%, whereas the fill factor and open circuit voltage are maintained the same. The proposed multi-junction solar cell has reported the highest power conversion efficiency of 44.397% among the III-V triple junction solar cells designed already. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two new gallium phosphate/phosphite-oxalates hybrid solids, {[H 2 dmpip][Ga 2 (HPO 4 ) 2 (PO 4 )(C 2 O 4 ) 0.5 ]·H 2 O} ( 1 ) and [H 2 apm][Ga 2 (H 2 PO 3 ) 2 (HPO 3 ) 2 (C 2 O 4 )] ( 2 ), where dmpip = 2,6-dimethyl-piperazine and apm = N-(3-aminopropyl)morpholine, have been synthesized and structurally characterized. Both of compounds 1 and 2 are formed by the connectivity of the Ga-based polyhedral, phosphite/phosphate groups as well as oxalate units. Compound 1 possesses a two-dimensional layer structure, in which the C 2 O 4 units via an in-plane linkage connect two Ga center within the sheet. While in 2 , the C 2 O 4 units serve as bis-bidentates ligands bridging two GaO 6 octahedra from two distinct gallium-phosphite chains to give rise to inorganic-organic hybrid layer with 8-membered rings. In these materials, the structure-directing amines reside in the interlayer region and interact with the layers by way of hydrogen-bonds. [ABSTRACT FROM AUTHOR]

Nanowires hold great promise as tools for probing and interacting with various molecular and biological systems. Their unique geometrical properties (typically <100 nm in diameter and a few micrometers in length) enable minimally invasive interactions with living cells, so that electrical signals or forces can be monitored. All such experiments require in situ high-resolution imaging to provide context. While there is a clear need to extend visualization capabilities to the nanoscale, no suitable super-resolution far-field photoluminescence microscopy of extended semiconductor emitters has been described. Here, we report that ground state depletion (GSD) nanoscopy resolves heterostructured semiconductor nanowires formed by alternating GaP/GaInP segments ("barcodes") at a 5-fold resolution enhancement over confocal imaging. We quantify the resolution and contrast dependence on the dimensions of GaInP photoluminescence segments and illustrate the effects by imaging different nanowire barcode geometries. The far-red excitation wavelength (~700 nm) and low excitation power (~3 mW) make GSD nanoscopy attractive for imaging semiconductor structures in biological applications. [ABSTRACT FROM AUTHOR]

In this paper, Al-doped ZnO (AZO) grown by metal-organic chemical vapor deposition (MOCVD) using H2O as an oxidizer was employed as a transparent conductive layer (TCL) in AlGaInP-based light-emitting diodes (LEDs). A direct ohmic contact structure was observed between the AZO and the carbon-doped p+-GaP (p+-GaP:C) contact layer with a specific contact resistance of \mathsf 2.2 \times \mathsf 10^\mathsf -4 cm $^{{\mathsf {2}}} . It is attributed to the unintentional hydrogen-doped n++-AZO interfacial layer at the clear interface of the AZO/p+-GaP:C. A forward voltage ( Vf ) of 1.99 V at 20 mA was achieved, which is lower than that of the ITO-TCL LED with a Vf of 2.07 V. In addition, compared with the conventional LED without TCL and the ITO-TCL LED, the studied LED demonstrates high output power and high wall-plug efficiencies. These results indicate that the AZO-TCL grown by MOCVD using H2O as an oxidizer is an effective current spreading layer for high-performance AlGaInP-based LED application. [ABSTRACT FROM PUBLISHER]

The current-voltage ( I-V ) characteristics of Au/ n -GaP Schottky barrier diode was analyzed in wide temperature range of 220–400 K. The conduction mechanism in the low bias region, except for 220 K and 240 K, was identified as tunneling (TN). Nevertheless, thermionic emission (TE) becomes dominant as the voltage increases. The diode parameters were evaluated in this region by TE model incorporating the concept of thin insulating layer. The series resistance ( R s ) of the device was found to decrease with increase in temperature. In the 220–320 K temperature range, as reported for most of the Schottky diodes, the zero-bias barrier height ( ϕ b0 ) decreases and the ideality factor ( η ) increases with the decrease of temperature. The value of modified Richardson constant ( A** ) obtained agrees well with the theoretical value. However, in the 320–400 K range, the variation of η and ϕ b0 with temperature shows opposite trend, which is speculated as due to the change in conduction pattern by the temperature induced modifications at the interface. [ABSTRACT FROM AUTHOR]

The bond models are presented that explain the S -type anomaly of GaP LEDs’ electrical characteristics at temperatures Т ≤ 120 K. A possible mechanism of negative differential resistance appearing in current-voltage characteristics is proposed, based on the features of the gallium phosphide complex band structure. The conductive zone absolute minimum in this crystal is near the Brillouin zone end. Due to the positive internal bond, controlled by the current, intervalley electron transfer occurs from the side valley to the higher one with the smaller effective electron mass. While the applied voltage is increased, electrons move from the lateral valley to the direct conductive zone bottom and an S -type negative differential resistance region appears. [ABSTRACT FROM AUTHOR]

This paper presents a thin nanocrystalline ZnO layer with embedded GaP nanowires (NWs). The NWs were grown in vapour-liquid-solid (VLS) mode by metal organic vapour phase epitaxy (MOVPE) at Au seeds formed from a very thin Au layer. The NWs were finally embedded in ZnO using deposition by RF sputtering combined with etching steps that resulted in a compact antireflection layer. We studied properties of such compact NWs structure by means of x-ray diffraction and atomic force microscopy. The study of mechanical properties was performed by nanoindentation measurements. The nanoindentation measurement showed that the incorporation of GaP nanowires into a ZnO layer led to increased hardness compared with that of a pure ZnO layer. The compact GaP NW/ZnO layer structure also exhibited some degree of pseudoelasticity. In addition, the mechanical properties of the compact nanowire layer are sufficiently robust to allow the thermo-compression bonding on the top of the structure. [ABSTRACT FROM AUTHOR]

GaP nanowires (NWs) were grown on a Si substrate by gas source molecular beam epitaxy using self-assisted growth. Selective-area growth was achieved using a patterned oxide mask. Periodic GaAsP marker layers were introduced during growth to study the growth progression using transmission electron microscopy. We demonstrate control of the NW morphology via the V/III flux ratio, the pattern pitch, and the oxide hole diameter. As the V/III flux ratio was increased from 1 to 6, the NWs showed a reduced top diameter and increased height. Reduced oxide hole diameter and increased V/III flux ratio caused the Ga droplet to be consumed partway through the growth for some NWs, leading to a switch from VLS group V limited growth to diffusion limited growth. [ABSTRACT FROM AUTHOR]

The high pressure behavior of gallium phosphide, GaP, has been examined using the synchrotron X-ray diffraction technique in a diamond anvil cell up to 27 GPa and 900 K. The transition from a semiconducting to a metallic phase was observed. This transition occurred at 22.2 GPa and room temperature, and a negative dependence of temperature of this transition was found. The transition boundary was determined to beP(GPa) = 22.6 − 0.0014 × T(K). [ABSTRACT FROM AUTHOR]

Thermal behavior and carrier injection of GaAs/GaP quantum-dot light-emitting diodes are investigated. The diodes emit red light between 1.8 eV and 2 eV and operate at room temperature. Adding aluminum to the quantum structures shifts the emission wavelength towards green. Thermal filling and high injection of the carriers in GaAs/GaP quantum dots result in contributions of different radiative recombination channels with higher emission energies and hence a blueshift of the electroluminescence with increasing temperature and very small thermal quenching of the light output. [ABSTRACT FROM AUTHOR]

A new type of composite antireflection coating based on a compact GaP NW/ZnO layer structure is presented. The structure was prepared by a combination of Metal Organic Vapour Phase Epitaxy (MOVPE) with RF sputtering. The former was used to grow GaP nanowires and the latter to deposit ZnO nanograins on them. The nanowires were completely engulfed by a compact ZnO layer without voids. This was achieved with a carefully optimised technique that alternated ZnO deposition and ZnO etching by argon ions. The compact structure showed a significant decrease in reflectance compared with reflectance at the GaP substrate or at the GaP substrate with the GaP NWs. Nanoindentation measurements indicated that the micro-hardness of such a compact GaP NW/ZnO layer structure was better than that of the pure ZnO layer. The structure also exhibited some degree of pseudoelasticity. [ABSTRACT FROM AUTHOR]

We studied the process of deposition of a thin nanocrystalline ZnO layer on vertical free-standing GaP nanowires (NWs). The paper presents the preparation of a new type of composite antireflection coating based on a compact GaP NW/ZnO layer structure. The NWs were prepared using metal organic vapour phase epitaxy. They were grown at Au seeds created from a ∼0.3 nm thick Au layer, which was deposited on GaP substrate by evaporation. RF sputtering was used to cover the NWs and substrate with a ZnO layer with a nominal thickness between 50 and 250 nm. While thinner ZnO layers wrapped the NWs and covered the substrate, thicker ones also filled the volume between the NWs and the ZnO wrapping acquired a shape that resembled that of cotton swabs. A compact and planarized GaP NW/ZnO layer structure was achieved by altering ZnO deposition with ZnO etching by Ar ions. GaP NW/ZnO layer structures, which differed in the degree of ZnO filling, exhibited antireflection behaviour that was superioir to that of GaP substrate with GaP NWs. [ABSTRACT FROM AUTHOR]

We present all-dielectric gallium phosphide (GaP) nanoantennas as an efficient nanophotonic platform for surface-enhanced second harmonic generation (SHG) and fluorescence (SEF), showing negligible losses in the visible range. Employing single GaP nanodisks, we observe an increase of more than 3 orders of magnitude in the SHG conversion signal in comparison with the bulk. This constitutes an SHG efficiency as large as 0.0002%, which is to the best of our knowledge the highest yet achieved value for a single nano-object in the optical region. Furthermore, we show that GaP dimers with 35 nm gap can enhance up to 3600 times the fluorescence emission of dyes located in the gap of the nanoantenna. This is accomplished by a fluorescence lifetime reduction of at least 22 times, accompanied by a high-intensity field confinement in the gap region. These results open new avenues for low-loss nanophotonics in the optical regime. [ABSTRACT FROM AUTHOR]

In the present work, the effects of swift silver ion irradiation in crystalline gallium phosphide samples with various fluences ranging between 1 × 10 11 and 2 × 10 13 ions cm −2 have been described. Atomic force microscopy images of the samples irradiated with different fluences showed the existence of hillocks at the surface, the diameter and density of these clusters were found to be depend on the ion fluence. As the ion fluence increased (⩾1 × 10 13 ions cm −2 ), the big size hillocks having arbitrary shapes were observed due to outflow of the molten material to the sample surface or defect induced swelling of track areas accumulated during the track overlapping. Phonon confinement model employed to first order Raman scattering from longitudinal optical phonon mode revealed the decrease in phonon coherence length from 73.0 nm to 23.7 nm with the increase in ion fluence from 1 × 10 12 to 2 × 10 13 ion cm −2 . [ABSTRACT FROM AUTHOR]

The impact of energy loss mechanism by 100 MeV Au 8 + ion on the dielectric parameters of Ni/oxide/n-GaP Schottky diode was studied under different fluences. The Schottky barrier height, donor ion concentration and interface states density of the diode were varied considerably under different ion fluence. The various dielectric parameters were altered significantly by the ion fluence. The reduction in dielectric constant after irradiation was ascribed to screening of space charge polarization due to reduction in interface states density. The relaxation peak of imaginary electric modulus indicates hopping type conduction mechanisms in the intermediate voltage range. The sensitive behavior of dielectric parameters with fluence dose was attributed to the alteration of interface state density due to high electronic energy loss of 100 MeV Au 8 + ions at the interface. [ABSTRACT FROM AUTHOR]

The in-situ capacitance-frequency and conductance-frequency measurements of 100 MeV Au 8+ swift heavy ion irradiated Ni/n-GaP Schottky structure at a constant bias voltage have been carried out in the frequency range 1 kHz–1 MHz at room temperature. The interface states density and the relaxation time of the charge carriers have been calculated from Nicollian and Brews method. Various dielectric parameters such as dielectric constant, dielectric loss, loss tangent, series resistance, ac conductivity, real and imaginary parts of electric modulus have been extracted and analyzed under complex permittivity and complex electric modulus formalisms. The capacitance and conductance characteristics are found to exhibit complex behaviors at lower frequency region (1–20 kHz) for all the samples. The observed peaks and dips at low frequency region are attributed to the relaxation mechanisms of charge carriers and the interface or dipolar polarization at the interface. The dielectric properties are found to be effectively changed by the ion fluence which is attributed to the variation in interface states density and their relaxation time. [ABSTRACT FROM AUTHOR]

Angle-resolved electron Rutherford backscattering (ERBS) measurements using an electrostatic electron energy analyser can provide unique access to element-resolved crystallographic information. We present Kikuchi pattern measurements of the non-centrosymmetric crystal GaP, separately resolving the contributions of electrons backscattered from Ga and P. In comparison to element-integrated measurements like in the method of electron backscatter diffraction (EBSD), the effect of the absence of a proper 4-fold rotation axis in the point group of GaP can be sensed with a much higher visibility via the element-resolved Ga to P intensity ratio. These element-resolved measurements make it possible to experimentally attribute the previously observed point-group dependent effect in element-integrated EBSD measurements to the larger contribution of electrons scattered from Ga compared to P. [ABSTRACT FROM AUTHOR]

Emerging technologies for integrated optical circuits demand novel approaches and materials. This includes a search for nanoscale waveguides that should satisfy criteria of high optical density, small cross-section, technological feasibility and structural perfection. All these criteria are met with self-assembled gallium phosphide (GaP) epitaxial nanowires. In this work, the effects of the nanowire geometry on their waveguiding properties are studied both experimentally and numerically. Cut-off wavelength dependence on the nanowire diameter is analyzed to demonstrate the pathways for fabrication of low-loss and subwavelength cross-section waveguides for visible and near-infrared (IR) ranges. Probing the waveguides with a supercontinuum laser unveils the filtering properties of the nanowires due to their resonant action. The nanowires exhibit perfect elasticity allowing fabrication of curved waveguides. It is demonstrated that for the nanowire diameters exceeding the cut-off value, the bending does not sufficiently reduce the field confinement promoting applicability of the approach for the development of nanoscale waveguides with a preassigned geometry. Optical X-coupler made of two GaP nanowires allowing for spectral separation of the signal is fabricated. The results of this work open new ways for the utilization of GaP nanowires as elements of advanced photonic logic circuits and nanoscale interferometers., (© 2023 Wiley-VCH GmbH.)

Optically addressable solid-state defects are emerging as some of the most promising qubit platforms for quantum networks. Maximizing photon-defect interaction by nanophotonic cavity coupling is key to network efficiency. We demonstrate fabrication of gallium phosphide 1-D photonic crystal waveguide cavities on a silicon oxide carrier and subsequent integration with implanted silicon-vacancy (SiV) centers in diamond using a stamp-transfer technique. The stamping process avoids diamond etching and allows fine-tuning of the cavities prior to integration. After transfer to diamond, we measure cavity quality factors ( Q ) of up to 8900 and perform resonant excitation of single SiV centers coupled to these cavities. For a cavity with a Q of 4100, we observe a 3-fold lifetime reduction on-resonance, corresponding to a maximum potential cooperativity of C = 2. These results indicate promise for high photon-defect interaction in a platform which avoids fabrication of the quantum defect host crystal.

Planar GaP epilayers on Si(111) are considered as virtual substrates for III-V-related optoelectronic devices such as high-efficiency nanowire-based tandem absorber structures for solar energy conversion, next generation LEDs, and fast photodetectors. Rotational twin domains in such heteroepitaxial epilayers are found to strongly impede vertical nanowire growth. We investigate the twin-induced defect density and surface morphology of B-type GaP/Si(111) virtual substrates in dependence on the GaP nucleation process by metalorganic chemical vapor deposition. By employing quantitative high-resolution X-ray diffraction (HR-XRD)), scanning electron and atomic force microscopy (SEM and AFM), we reveal the significant influence of nucleation temperature and substrate miscut direction on the formation of rotational twin domains during a two-step GaP growth approach. The epilayer defect density is drastically decreased by low temperature GaP nucleation on Si(111) misoriented 3° toward [112], where rotational twin domains are suppressed below 5% and the layers exhibit a smooth surface morphology. We demonstrate that these virtual substrates are highly suitable for vertical GaP nanowire growth. [ABSTRACT FROM AUTHOR]

Local electrical properties of the surface of porous GaP have been measured by the method of tunneling spectroscopy in ultrahigh vacuum. Two surface areas with different electrical properties were found. The effect of anomalous field-induced photoemission was observed. The most probable reason for this effect is the presence of GaO and GaP nanoclusters and the high density of acceptor-type surface states associated with these clusters. Integral characteristics of the field electron emission from the sample surface were obtained by using a computerized recording system with online processing of current-voltage characteristics. [ABSTRACT FROM AUTHOR]

This study reports the optoelectronic characteristics of ZnO/GaP buffer/CuO-Cu2O complex (COC) inverse heterostructure for solar cell applications. The GaP and COC layers were used as buffer and absorber in the cell structure, respectively. An energy gap widening effect and CuO whiskers were observed as the copper (Cu) layer was exerted under heat treatment for oxidation at 500 °C for 10 min, and arose from the center of the Cu2O rods. For preparation of the 30 nm-thick GaP buffer by sputtering from GaP target, as the nitrogen gas flow rate increased from 0 to 2 sccm, the transmittance edge of the spectra demonstrated a blueshift form 2.24 to 3.25 eV. Therefore, the layer can be either GaP, GaNP, or GaN by changing the flow rate of nitrogen gas.

Microplasma breakdowns of red and green GaP diodes were studied. It has been shown that tunneling was the main component of reverse current at the beginning of the breakdown while an avalanche current prevailed at highs breakdown current. Microplasma spectrum is considered to be the result of the overlapping of hot carrier emitting and recombination amitting of impurity level-valence band. 2 MeV electron irradiation leads to the de-crease of microplasma number due to the radiation defect creating.

High–pressure phase stability of gallium phosphide was explored under different hydrostatic environments up to 40.0 GPa in a diamond anvil cell. Two irreversible phase transitions from the semiconductor to metal to an amorphous state appear at 19.8 and 31.5 GPa and as well as 22.6 and 35.3 GPa under nonhydrostatic and hydrostatic environments, respectively. Furthermore, the hysteresis effect of the high–pressure phase transition of a sphalerite–structure compound under a hydrostatic environment was disclosed. All of the obtained results can provide new insight into the underlying structural evolution and electrical transport characteristics for the semiconducting compound at different hydrostatic environments. [ABSTRACT FROM AUTHOR]

An algorithm for the simulation and analysis of the parameters that determine the sensitivity of the photodiode surface-barrier structures based on n+—n-GaP—SnO2(F) has been developed. It has been shown that the monochromatic current sensitivity to radiation at wavelength of 250 nm in such a structure can reach 0,1—0,12 A/W.

The contact of water with semiconductors typically changes its surface electronic structure by oxidation or corrosion processes. A detailed knowledge—or even control of—the surface structure is highly desirable, as it impacts the performance of opto-electronic devices from gas-sensing to energy conversion applications. It is also a prerequisite for density functional theory-based modelling of the electronic structure in contact with an electrolyte. The P-rich GaP(100) surface is extraordinary with respect to its contact with gas-phase water, as it undergoes a surface reordering, but does not oxidise. We investigate the underlying changes of the surface in contact with water by means of theoretically derived reflection anisotropy spectroscopy (RAS). A comparison of our results with experiment reveals that a water-induced hydrogen-rich phase on the surface is compatible with the boundary conditions from experiment, reproducing the optical spectra. We discuss potential reaction paths that comprise a water-enhanced hydrogen mobility on the surface. Our results also show that computational RAS—required for the interpretation of experimental signatures—is feasible for GaP in contact with water double layers. Here, RAS is sensitive to surface electric fields, which are an important ingredient of the Helmholtz-layer. This paves the way for future investigations of RAS at the semiconductor–electrolyte interface.